Convert JsonWriter::Write to taking a const ref for the in-param

components/dom_distiller/core/page_features_unittest.cc

Index: components/dom_distiller/core/page_features_unittest.cc
diff --git a/components/dom_distiller/core/page_features_unittest.cc b/components/dom_distiller/core/page_features_unittest.cc
index 413c55f7b4e8d3f1ba33da711277aced107a8884..1fee593421a333861016b7090211248961cec1c1 100644
--- a/components/dom_distiller/core/page_features_unittest.cc
+++ b/components/dom_distiller/core/page_features_unittest.cc
@@ -70,7 +70,7 @@ TEST(DomDistillerPageFeaturesTest, TestCalculateDerivedFeatures) {
     // CalculateDerivedFeaturesFromJSON expects a base::Value of the stringified
     // JSON (and not a base::Value of the JSON itself)
     std::string stringified_json;
-    ASSERT_TRUE(base::JSONWriter::Write(core_features, &stringified_json));
+    ASSERT_TRUE(base::JSONWriter::Write(*core_features, &stringified_json));
     scoped_ptr<base::Value> stringified_value(
         new base::StringValue(stringified_json));
     std::vector<double> derived(